feat(build): implement release-ready build outputs and file manifest for Obsidian plugin

[cto-new]

Summary

Introduce a release-ready build flow that outputs all plugin assets to the build/ directory and generates a release manifest suitable for Obsidian plugin import.

Details

• Update esbuild.config.mjs to emit main.js, styles.css, and styles_modern.css to build/, and copy manifest.json and versions.json into build/
• Generate release-files.txt in build/ listing all required release files
• Enable production minification for builds
• Update release script to reflect release assets location and display manifest
• Align docs to reference build/ outputs for Obsidian import

No breaking changes. Migration: none required.